I'm rooting for Couture but I predict Lesnar. He's huge and he has great takedowns. A lot of guys like to remind us that Sylvia is huge too. Sylvia isn't a takedown threat, he stands on the outside and picks you apart. Also, Couture doesn't really have much of a submission game, which makes him less dangerous to a submission rookie like Lesnar.
I predict this fight will involve a lot of time on the ground with Lesnar on top. I hope I'm wrong.